1. Field of the Invention
The present invention relates to an inkjet printing apparatus and detection method for detecting the discharge state of a nozzle.
2. Description of the Related Art
In an inkjet printing apparatus which prints by discharging ink droplets from orifices and adhering them to a printing medium such as paper or a plastic film, the printhead includes heaters configured to generate heat energy for discharging ink. An electrothermal transducer which generates heat in accordance with energization, a driving circuit, and the like can be formed by a step similar to a semiconductor manufacturing process. High-density mounting of nozzles is easy, and high-resolution printing can be implemented.
However, a discharge failure may occur in all or some nozzles of the printhead owing to clogging of a nozzle by a foreign substance, highly viscous ink, or the like, a bubble entering the ink supply path or nozzle, a change of the wettability of the nozzle surface, or the like. To prevent degradation of the image quality when such a discharge failure occurs, it is important to quickly execute a recovery operation of recovering the discharge state of a nozzle, and a complementary operation using another nozzle or the like. However, to quickly perform these operations, the discharge state and generation of a discharge failure need to be determined at high accuracy.
Japanese Patent Laid-Open No. 2008-23987 discloses a method of detecting a temperature drop generated in normal discharge in order to detect a discharge failure. In normal discharge, a point (temperature drop rate change point) appears, at which the temperature drop rate changes a predetermined time after the detected temperature reaches a maximum temperature. However, when a discharge failure occurs, this point does not appear. Based on the difference in temperature waveform, the ink discharge state is determined. A detector which detects the temperature is arranged below a heater which generates heat energy for discharge. By supplying a constant current to a resistor serving as the detector, a change of the resistance value upon a change of the temperature is output as a voltage value.
However, in Japanese Patent Laid-Open No. 2008-23987, the temperature drop rate change point necessary to detect a discharge state arises from contact of a small amount of ink upon normal discharge. Thus, a change of the signal at the temperature drop rate change point is very small. If the entire temperature waveform which changes upon applying energy to the heater is designed to fall within the input range of a subsequent A/D converter (ADC), the small signal change at the temperature drop rate change point becomes smaller. Such a small change is highly likely to be buried in noise or the like, and it becomes very difficult to determine the discharge state.